There are several methods for injecting fuel into an internal combustion engine. One of these methods is gasoline direct injection (GDI), in which a direct injection injector injects fuel directly into a combustion chamber. Another method is multi-point injection (MPI), in which a port injection injector provided in each intake port of a multi-cylinder engine injects fuel toward intake air in the intake port.
JP2013-036447A, published by the Japan Patent Office in 2013, proposes fuel injection control for an internal combustion engine of a vehicle that comprises both a direct injection injector and a port injection injector. Specifically, in a low load operation region (a first execution range) of the internal combustion engine, fuel injection is executed using the port injection injector alone, and in an operation region (a second execution range) on a high load side of the first execution range, fuel injection is executed using the direct injection injector. More specifically, within the second execution range, in a low load region in which the engine load is comparatively low, fuel is injected from both the port injection injector and the direct injection injector, and in a high load region in which the engine load is high, fuel is injected from the direct injection injector alone.
According to this prior art, when the internal combustion engine decelerates from the second execution range, fuel is injected from both the direct injection injector and the port injection injector until the engine load reaches the first execution range. A fuel pressure of the direct injection injector typically increases as the engine load increases, and therefore, if fuel is injected from the port injection injector as well as from the direct injection injector when the internal combustion engine decelerates, the fuel pressure of the direct injection injector remains high.
When the internal combustion engine switches to acceleration while the fuel pressure is high, it is difficult to control the fuel injection amount to a small amount using the direct injection injector. In a case where the control of the prior art is employed, therefore, the amount of fuel injected when fuel injection by the direct injection injector is resumed inevitably increases as the engine load increases.